## What changed
Add an end-to-end core test that compresses a parent and forked child rollout,
then resumes the child through paginated history loading. Verify that the
resumed model input:
- retains the persisted compaction checkpoint and inherited history;
- includes child history through the fork boundary;
- excludes obsolete pre-checkpoint and post-fork parent messages; and
- reads the compressed ancestor without materializing its JSONL file.
GitOrigin-RevId: 1624c4d844345fe2671436f37bc39b3e59fb3dea
